1. Field of the Invention
This invention relates to an ink composition and an image recording method. More specifically, this invention pertains to an ink composition particularly suited for an ink jet printer and to an image recording method using the composition.
2. Description of the Related Art
Recently, ink jet printers, which have a low running cost and can easily provide high resolution images and color images, have come to be used as output devices for information processing equipment such as computers. As an ink composition for an ink jet printer, an aqueous solution of a dye has been used mainly to date. However, in the aqueous solution of a dye, when ink discharged from a nozzle is deposited on recording paper, the ink blots on the recording paper and a dot is larger than the ink droplet discharged and the density of the image recorded becomes low. In addition, it has the problem that the recorded image is less waterproof.
With a view to overcoming these problems of the aqueous ink for ink jet system, A! proposed are ink compositions to which resin particles for forming a film are added JP-B No. 60-32663 (addition of a latex), JP-A No. 5-239392 (addition of a resin containing a carboxyl group and a nonionic hydrophilic group and dispersible in water), JP-A No. 5-255628 (addition of an non-crosslinked vinyl polymer) and JP-A No. 6-340835 (addition of polyester particles containing an ionic group)!; and an ink composition to which colored resin particles capable of forming a film are added JP-A No. 5-255567!. B! Also proposed is an ink composition to which resin particles (polyester particles or the like) and a crosslinking agent are added respectively so as to obtain an image film composed of crosslinked resin JP-B No. 7-47355!.
The ink compositions described above A! can not prevent the ink blotting due to the capillary phenomenon of the fiber of the recording paper completely. The ink compositions described above A! can not also prevent the penetration of the ink into the recording paper and then improvement of the image density is limited. Moreover, the above-described ink compositions A! to which particles capable of forming a film at normal temperature are added have the common problem that the image recorded on the substrate becomes sticky when the ambient temperature around the printed sample becomes high. The reason why the image becomes sticky when the ambient temperature is high is that resin particles whose glass transition temperature is lower than normal temperature must be used so that the resin particles can coalesce at the temperature equal to or lower than the normal temperature so as to form a film. The image becoming sticky is remarkable at particularly high environmental temperatures.
In the above-described ink composition B!, the image recorded does not become sticky because the image film has been crosslinked. However, the crosslinking agent added to the ink composition is a reactive substance, thereby the ink composition has problems concerning safety and stability.
The present invention has been completed to dissolve the problems described above. An object of the present invention is to provide an ink composition which can prevent the ink blotting on the recording paper and can provide an image having markedly high density and water resistance, particularly to provide an ink composition suited for use in an ink jet printer.
Another object of the present invention is to provide an ink composition which does not become sticky after forming an image even at a high environmental temperature and involves no problem even in safety and stability.
A further object of the present invention is to provide an image recording method using such an ink composition.